Method of coupling tubes or pipes, and couplings or the like obtained by implementing the method

ABSTRACT

Tubes or pipes are engaged on an insert and are fixed thereon in sealed manner by molding a plastics material at least over those zones of said tubes or pipes that co-operate with said insert. The plastics material is molded so as to form a cellular material whose expansion is performed so as to give rise to compression forces on said tubes or pipes that ensure that said tubes or pipes are fixed or sealed onto the insert.

This application is a divisional of application Ser. No. 08/086,200,filed Jul. 1, 1993 now U.S. Pat. No. 5,460,762.

The invention relates to a method coupling tubes or pipes, and also tocouplings and like devices obtained by implementing the method.

BACKGROUND OF THE INVENTION

The invention is applicable to manufacturing devices such as branchcouplings for flexible tubes or pipes, in particular hoses based onrubber, on plastomers, or on elastomer thermoplastic, and it is alsoapplicable, under certain conditions, to manufacturing such couplingsfor tubes or pipes that are somewhat more rigid. The invention alsoextends to manufacturing devices for fixing such tubes or pipes toendpieces, and to manufacturing branches, tapping points, or bundles ofducts in such materials, without the above list being exhaustive. Thefields in which the invention may be implemented and where it may benecessary to couple to tubes or pipes together, include for example:building, home appliances, and the vast field of transportation-relatedindustries, in particular the car industry.

In the car industry, rubber-based hoses, and particularly but notexclusively those placed between the engine and the radiator to make upthe cooling circuit for the engine, and similarly the bundles forconveying various different fluids (hydraulic or pneumatic fluids suchas brake liquid, fuel, etc. . . . ) frequently include branching pointsthat serve either to establish secondary circuits from a main circuitsuch as stub ducts, branch links, etc. . . . , or else to enable controland/or monitoring functions to be performed such as measuring flow rateor temperature by means of probes, tapping points, etc. Such branchpoints, referred to below overall by the very general term "couplings orthe like" have long been manufactured by engaging the tubes or pipes tobe coupled on an insert of appropriate shape and then fixing said tubesor pipes to the insert by means of a very wide variety of types ofclamping collar. That long-established technique has progressively beenovertaken by crimping techniques as described in DE-3 729 057 or bytechniques in which rubber or plastic is overmolded, as explained inFR-A-2 549 196 or FR-A-2 610 073, for example. Although the more recenttechniques give satisfaction and enable devices to be obtained that arein widespread use, they can nevertheless sometimes be too expensiveand/or too difficult to implement in certain configurations, when thetechnique is crimping; or they require manufacturing time that isrelatively long (when overmolding rubber); or they make use ofmanufacturing techniques that can be complicated, as when overmoldingwith common plastics.

OBJECTS AND SUMMARY OF THE INVENTION

Consequently, a general object of the invention is to provide a methodof coupling tubes or pipes that is very easily implemented whilenevertheless guaranteeing the quality of the resulting couplings anddevices, in particular with respect to absence of leakage of the fluidflowing along such tubes or pipes, particularly when the fluid is underpressure.

Another object is the invention is to provide such a method enablingcouplings or the like to be obtained in complex shapes, regardless ofthe tubes or pipes constituting said couplings or the like, and to dothis at low cost, in spite of the complexity of such devices.

Another object of the invention is to provide such a method that doesnot require special manufacturing machines for its implementation andthat can also be performed using short manufacturing cycles that aretherefore favorable to obtaining high productivity.

It is also an object of the invention to provide such a method enablingcouplings or like devices to be obtained directly that are ofsatisfactory appearance, thereby making them more acceptable to users.

The above objects and others are achieved in a method of coupling tubesor pipes, in particular tubes or pipes based on rubber, on plastomers,or on elastomer thermoplastics, in which said tubes or pipes are engagedon an insert and are held thereon in sealed manner by molding a plasticmaterial at least over zones where said tubes or pipes co-operate withsaid insert, and in which said plastics material is molded in such amanner as to form a cellular material whose expansion is performed insuch a manner as to give rise to pressure forces on said tubes or pipesthat ensure that said tubes or pipes are fixed in sealed manner on theinsert.

For molding the plastics material which is advantageously performed byinjection techniques, such a method makes it possible to use aninjection press with tooling and in particular molds as ordinarily usedfor manufacturing cellular materials.

The method is applicable to tubes or pipes that are optionallyreinforced and/or optionally covered with an outer textile sheath andmakes it possible to shape the couplings or the like as a function ofpractical requirements, e.g. to provide branch connections or tappingpoints simultaneously on one or more tubes or pipes whileinterconnecting said tubes or pipes by bridging so as to obtain anassembly such as a bundle of tubes or pipes suitable for handling as aunit assembly.

The method also makes it possible, at the place where the plasticsmaterial is molded, to unite tubes or pipes that are long and that couldnot or could only with difficulty be united by the techniques ofovermolding rubber, e.g. because of the sizes of vulcanizing autoclaves.

The method also makes it possible to secure parts such as pressuregauges, temperature probes, flow rate meters, drain means, etc. to saidtubes or pipes in a single operation with and at the same time as thecouplings proper are made on said tubes or pipes.

In a first implementation, the method of the invention provides forforming the cellular material by incorporating an inert gas or a liquidhaving a low boiling point in the injected polymer material.

In such an implementation, the mixture of plastics material and inertgas or low boiling point liquid is conveyed by means of a screwtransporter device into an accumulator where the mixture is kept underpressure to prevent premature expansion, and then after a retainingshutter has been opened rapidly, a moving piston in the accumulatorinjects the mixture at high speed into the mold. After the mold has beenfilled, a valve member is closed and expansion takes place inside themold while the accumulator is being refilled for a subsequent injectioncycle.

In another implementation, the plastics material is expanded and thecellular material is formed as a result of a chemical pore-generatingagent or inflating agent that decomposes at the molding temperature. Theagent is selected as a function of the injected plastics material so asto avoid chemical interactions with said material, and so as to takeaccount of implementation temperatures, of possible reactions with thematerial from which the mold is made, of the nature of the gaseousproducts, etc. . . . .

In an advantageous embodiment, and when the injected plastics materialis of the polyamide type, said inflating agent is selected from thefamily of azodicarbonamides or from the family of tetrazoles, and it isadded to the plastics material during a preliminary operation or duringthe injection process.

Since this implementation using an inflating agent is simpler to performthan the implementation using an inert gas or a low boiling pointliquid, and since it is performed using ordinary injection machines, itis preferred. It also makes it possible to obtain better control overthe regularity and the uniformity of the products obtained, inparticular with respect to the density of the cellular material, thedensity gradient between the skin and the core of said material, and thesize and distribution of the cells, while simultaneously conferring asatisfactory surface state to the manufactured device, particularly wheninjection is performed at medium to high pressure.

A coupling or like device for tubes or pipes, in particular tubes orpipes made of rubber, plastomers, or elastomer thermoplastics,comprising at least one insert on which the tubes or pipes are engaged,and a molding of plastics material that encloses in sealed manner atleast those portions of said tubes or pipes that co-operate with theinsert, is characterized, according to the invention, in that saidplastics material is in the form of a cellular material that is expandedand rigid and that exerts compression forces on said tubes or pipesensuring that said tubes and pipes are fixed or sealed on the insert.

The cellular material of the closed-cell rigid-foam type has an overalldensity that may lie in the range about one-third of the pure plasticsmaterial that is used, to said density of the pure plastics materialminus a few percent.

Thus, because of the presence of the cellular material, a coupling orlike device of the invention benefits from relatively low thermalconductivity, good resistance to shocks which are well absorbed by thecellular structure which reduces propagation of possible cracks, savingsin material, and a higher stiffness/weight ratio than that of knownprior devices. To increase the mechanical characteristics of couplingsor like devices of the invention, e.g. characteristics of rigidity,hardness, creep resistance, traction strength, or resistance todeformation under load, while improving its cellular structure, and alsowhile simultaneously reducing molding cycle times, the inventionprovides for reinforcing the cellular material with fillers,advantageously glass beads and/or fibers.

When fillers are used, they are present at a concentration lying in therange 5% to 95% by weight of the injected plastics material.

In a preferred embodiment, the fillers represent 5% to 25% by weight ofthe injected plastics material.

According to another characteristic of the invention, the injectionmolding of the plastics material is performed in such a manner that thecouplings or like devices have a surface skin in which the depth ofroughness is of the same order as that obtained when injection moldingcompact plastics material, i.e. of the order of a few microns.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be well understood from the following descriptiongiven by way of example and made with reference to the accompanyingdrawings, in which:

FIGS. 1 to 3 show the coupling method of the invention and show acoupling obtained by implementing the method; and

FIGS. 4 to 8 show other shapes of couplings obtained using the method ofthe invention.

MORE DETAILED DESCRIPTION

Reference is made initially to FIGS. 1 to 3 which are diagrams showingthe method of the invention for coupling together an endpiece and a tubeor pipe made of rubber, plastomer, or an elastomer thermoplastic. Asshown in FIGS. 1 and 2, the coupling method of the invention begins byengaging a tube or pipe 11 onto an insert 10, after which said tube orpipe is fixed to the insert and the fixing therebetween is sealed bymeans of a cellular material 12 molded onto the tube or pipe 11 in sucha manner as to give rise to compression forces on the said tube or pipe(as represented by arrows f in FIG. 2) that provide both said fixing andsaid sealing. To do this, the invention provides for placing the insert10 and the tube or pipe 11 inside a mold M (provided with at least onedevice i for injecting plastics material that opens out into the moldvia an injection sill s, and also provided with vent holes) and then ininjecting a polymer material into said mold where it is transformed, insitu, into a cellular material.

In a first implementation of the method, an inert gas such as nitrogen,or freon, or a low boiling point liquid such as a chlorinatedhydrocarbon is incorporated in the injected plastics material, themixture of plastics material and inert gas being kept under pressureuntil it is injected into the mold M where expansion takes placesimultaneously with cooling of the molded material. The material whichis confined in the mold "inflates" against the tube or pipe 11 to formthe cellular material 12 (FIG. 2) and in so doing develops compressionforces that are sufficient for ensuring fixing and sealing of the tubeor pipe on the insert.

In a second implementation which leads to the same result, the expansionof the plastics material to form the cellular material 12 is the resultof a chemical pore-generating agent or inflating agent decomposing atthe molding temperature. The agent is generally mixed with the injectedplastics material during a preliminary operation or during the injectionprocess or by compounding. In the first case, the inflating agent andthe plastics material may be mixed dry, or they may be mixed in a barreltogether with an adhesive agent, whereas in the second case the agent isinserted by means of automatic mixers and metering devices mounted onthe injection press, or in the third case the agent is inserted into themolten plastics material which, after being homogenized, is extruded andthen granulated to serve as raw material for the injection press feedingthe device i.

Whichever technique is implemented, performing the method by decomposingan inflating agent means that the quantity of material injected into themold is less than or at most equal to the volume of the mold cavity, andalso that the injection sills s are as small as possible and as close aspossible to the mold cavity, in contrast to the method used forinjecting a compact plastics material. In addition, injection isperformed in such a manner that the plastics material that is melted andtransported by the plastification screw remains under pressure so as toavoid premature expansion and the formation of gas bubbles, with thehighest possible retention of gas close to the outlet of the injectionnozzle being obtained by applying heat to said nozzle, where thedecomposition effect on the inflating agent of the added heat iscounterbalanced by an increase in pressure.

Injection is performed at high speed (likewise unlike the techniquesimplemented for molding compact plastics materials) with the cooling andretention time in the mold being selected so as to obtain a surface skinof satisfactory appearance, in particular a skin where the depth of itsroughness is of the same order as that obtained while injection moldingordinary plastics material, i.e. a few microns. The temperature of themold also contributes to obtaining a skin of good quality on thecellular material, insofar as the structure of the plastics materialdepends on its rate of crystallization which is itself a function of thetemperature gradient that is established between the mold and the moltenmaterial injected therein, whereas the size of the gas bubbles and thusof the cells is linked to the speed at which the injected materialcools.

Consequently, the invention proposes that the mold M should be providedwith channels C through which a regulating fluid is circulated (see FIG.3), thereby making it possible to give the inside wall of the mold p atemperature that is not too high, so as to facilitate crystallization,but which is not too low either so as to avoid the injected material"freezing" on its surface.

Given that obtaining a satisfactory cellular material depends not onlyon physical characteristics as mentioned above but also on the nature ofthe pore-generating inflating agent, the agent is selected so as to makeit possible to obtain an expanded cellular material that is rigid,having closed cells, obtained with good gas yield, without any risk ofchemical interaction between the polymer material and thepore-generating agent, and without any substances being evolved that aretoxic for manufacturing personnel or corrosive for the molds, thedecomposition temperature of the pore-generating agent also beingadapted to the shaping temperature of the injected polymer material.

Providing the above-mentioned conditions are satisfied, the method maybe implemented on tubes or pipes 11 of all types, that may optionally bereinforced, and that may optionally be coated in an outer textilesheath, and it may be performed with inserts 10 of a wide variety ofshapes and kinds, e.g. they may be made of metal, of optionallyreinforced plastics material, or of plastics material filled with fibersor the like.

In the embodiment shown in FIG. 3, a flexible tube or pipe 15, e.g. ahose made of a rubber based on EPDM, of plastomer, or of an elastomerthermoplastic material, is united with an endpiece 16 whose end portion17 is thinner than the remainder of the endpiece and has"Christmas-tree" projections 18 on its outside surface. When therelative dimensions of the inside diameter of the tube 15 and theoutside surface of the portion 17 of the endpiece ensures sufficientcohesion to enable the assembly of the tube fitted on the endpiece to behandled as a unit, said assembly is placed in the mold M. If cohesion isinsufficient, then the endpiece is provided with a weak adhesive priorto the tube being fitted thereon, and then, as before, the assembly isplaced in the mold M. After the polymer material plus the inflatingagent has been injected under the conditions explained above, a cellularmaterial 19 is obtained in the mold at a density that decreases from thedensity of its skin 20 (in contact with the mold, the endpiece 16, andthe tube 15) going towards its core 21, with the tube or pipe beingfixed in sealed manner on the endpiece as a result of the compressionforces exerted by the injected plastics material transforming into saidcellular material whose density may vary from about one-third that ofthe compact plastics material to substantially the density of thecompact material minus a few percent, with the variation being afunction of practical requirements concerning looked-for characteristicsof shock resistance, thermal conductivity, etc. . . . .

Since good results can be obtained with respect to fixing and sealing aflexible tube or pipe on an insert even at low densities, it maysometimes be advantageous to compensate for the decrease in certainmechanical characteristics due to the cellular nature of the material byadding fillers, in particular glass beads and/or fibers. Thus, by addingglass beads and/or fibers at concentrations lying in the range 5% to 95%by weight of the injected plastics material, it is possible to increasebending modulus, traction strength, and the temperature of deformationunder load, and the manufacturing cycle is shortened insofar as the skinof the cellular material takes less time to become sufficiently rigid toenable it to withstand the internal pressure developed during expansion.A preferred filler concentration lies in the range 5% to 25% by weightof the injected plastics material.

In the embodiment of FIG. 4, the invention is applied to couplingtogether two tubes or pipes 25 and 26 that are in alignment by means ofan insert 27 constituted by a tubular element whose end portions 28 and29 (end portion 29 having projections 30) co-operate with a middle zone31 to provide abutments 32 and 33 for positioning the tubes or pipes 25and 26. After the pipes have been engaged on the insert 27 so as tobring their ends into abutment against the abutments 32 and 33, saidtubes are fixed in sealed manner onto the insert by means of a sleeve 35of cellular material made in the manner described above. The couplingobtained in this way provides excellent characteristics of resistance tothe tubes being torn off the insert and of resistance to internalpressure, including during the pulse pressure cycles specified by carmanufacturers.

In the embodiment of FIG. 5, three tubes or pipes 40, 41, 42 are engagedon respective branches 43, 44, and 45 of a T insert 46 whose branch 43is advantageously provided with "Christmas-tree" projections 47. Thepipes are fixed in sealed manner on the insert by means of a sleeve 50of cellular material that envelops portions of the pipes over the zoneswhere they co-operate with the insert, and which also extends, as shownat 51, into the gap between the ends of the axially aligned pipes 43 and44.

In the embodiments of FIGS. 6 to 8, a tube or pipe 55, 55', or 55" basedon rubber, on plastomer, or on elastomer thermoplastic is fixed insealed manner on an endpiece 56, 56' or 56" projecting from a wall 57,57', or 57" which may be constituted, for example, by the wall of a carradiator water tank, or the like. Whether the endpiece is completelysmooth and cylindrical as shown at 56, or has a terminal rim 58 as shownin FIG. 7, or has "Christmas-tree" projections 59 as shown in FIG. 8,the tube or pipe 55, 55', or 55" is fixed in sealed manner on saidendpiece by means of a sleeve of cellular material 60 which is expandedin such a manner as to give rise to compression forces on the tube orpipe 55, 55' , or 55" that ensure that the tube or pipe is fixed insealed manner on the endpiece.

The invention is not limited to the embodiments described above but isapplicable to making devices such as bundles of tubes, drain valves, orfor installing measurement members such as pressure gauges, temperatureprobes, etc. in such devices.

Another application lies in coupling together tubes or pipes made ofmaterials that are not as flexible as rubber, providing that specialoperating conditions are then observed, for example relating to shape ortemperature, e.g. with temperature serving to soften to some extent thetubes or pipes that are to be assembled on an insert, etc. . . . .

Good results have been obtained by the method of the invention whenimplemented in the manner specified in the following non-limitingexamples.

EXAMPLE 1

Three polychloropropene pipes having an inside diameter of 5 mm wereconnected to a T insert of 6.6 polyamide reinforced with 30% glassfibers by engaging the pipes on the insert and then molding a 6,6polyamide containing 1.3% of an azodicarbonamide type inflating agentonto the resulting assembly.

With a mold temperature of about 80° C. and an injection temperature ofabout 30° C., the total duration of the manufacturing cycle was about 30seconds.

Six samples were then taken from the couplings made in this way andsplit into two groups of three couplings each, with the samples thenbeing subjected to pressure testing on a cyclically varying pulse testbench.

After the samples had been subjected to 25,000 cycles, the forcerequired for tearing the pipes off the insert was measured: the measuredvalues lay in the range 21.1 dan to 25.4 daN, about a mean value of 23.7daN.

EXAMPLE 2

T couplings like to those described in Example 1 but using pipes havingan inside diameter of 9 mm were made using a polymer material of the 6,6polyamide type including glass fibers constituting a 30% filler.

The polymer material filled in this way plus 1.3% of the same inflatingagent as used in Example 1 was then injected as in that example.

Two groups of three couplings each obtained in this way were thensubjected to tear-off tests after each of them had been subjected to25,000 cycles of dynamic pressure stresses.

The measured tear-off forces lay in the range 17.6 daN to 23.8 daN abouta mean value of 20.33 daN.

I claim:
 1. A coupling device for tubes or pipes made of rubber-typematerial, comprising at least one insert on which the tubes or pipes areengaged, and a molding of plastics material that encloses in sealedmanner at least those portions of said tubes or pipes that are engagedon the insert, wherein said plastics material is in the form of acellular material that is expanded and rigid and that exerts compressionforces on said tubes or pipes ensuring that said tubes or pipes arefixed and sealed on the insert and wherein the cellular material isreinforced by fillers.
 2. A coupling device according to claim 1,wherein the fillers constitute 5% to 95% by weight of the injectedplastics material.
 3. A coupling device according to claim 2, whereinthe fillers constitute 5% to 25% by weight of the injected plasticsmaterial.
 4. A coupling device according to claim 1, wherein thecellular material has a surface skin of roughness having a depth of theorder of about a few microns.
 5. A coupling device according to claim 1,wherein the density of the cellular material lies in the range of aboutone-third the density of pure plastics material to said density minus afew percent.
 6. A coupling device for a tube made of rubber-typematerial, comprising at least one tubular rigid insert on which aportion of the tube is engaged, and a molding of plastics material thatencloses in a sealed manner at least the said portion of the tube thatis engaged on the insert, wherein said plastics material is in the formof rigid cellular material that has been expanded around the portion ofthe tube and set within a mold and that has fixed and sealed the portionof the tube on the insert by the pressure resulting from the expansionof the cellular material in the mold.
 7. A coupling device according toclaim 6, wherein the cellular material is reinforced by fillers.
 8. Acoupling device according to claim 7, wherein the fillers constitute 5%to 95% by weight of the injected plastics material.
 9. A coupling deviceaccording to claim 8, wherein the fillers constitute 5% to 25% by weightof the injected plastics material.
 10. A coupling device according toclaim 6, wherein the cellular material has a surface skin of roughnesshaving a depth of the order of about a few microns.
 11. A couplingdevice according to claim 6, wherein the density of the cellularmaterial lies in the range of about one-third the density of pureplastics material to said density minus a few percent.
 12. A couplingdevice for tubes or pipes made of rubber-type material comprising atleast one insert on which the tubes or pipes are engaged, and a moldingof plastics material that encloses in sealed manner at least thoseportions of said tubes or pipes that are engaged on the insert, whereinsaid plastics material is in the form of a cellular material that isexpanded and rigid and that exerts compression forces on said tubes orpipes ensuring that said tubes or pipes are fixed and sealed on theinsert, wherein the cellular material has a surface skin of roughnesshaving a depth of the order of about a few microns.
 13. A couplingdevice for tubes or pipes made of rubber-type material, comprising atleast one insert on which the tubes or pipes are engaged, and a moldingof plastics material that encloses in sealed manner at least thoseportions of said tubes or pipes that are engaged on the insert, whereinsaid plastics material is in the form of a cellular material that isexpanded and rigid and that exerts compression forces on said tubes orpipes ensuring that said tubes or pipes are fixed and sealed on theinsert, wherein the density of the cellular material lies in the rangeof about one-third the density of the unexpanded plastics material tosubstantially said density.